P2BB0: Alternative Fuel Consumption Too Low
What to do
If you can smell gas, stop and have it inspected before driving on — treat any suspected CNG or LPG leak as a safety issue, not a running fault. Otherwise the car will typically fall back to petrol and drive normally; the cost of ignoring it is paying petrol prices and carrying an unused system. Have the gas side inspected by an installer qualified for it.
What this code means
The alternative fuel system is consuming less fuel than commanded.
A bi-fuel system meters its gaseous fuel as carefully as its petrol, and consumption is one of its self-checks. The module knows how much alternative fuel it commanded and what the tank level says was actually used; the two drifting apart means fuel is going somewhere unmetered, being delivered short, or being measured by a sensor that has stopped telling the truth.
Consumption too high deserves the most respect, because the unmetered somewhere can be a leak — and CNG or LPG leaks are a safety matter, not an economy one. Too low usually means delivery is being restricted or the level sensor is over-reporting; the empty-tank code is the honest end of the same measurement, usually meaning exactly what it says.
On a bi-fuel car the fallback hides the fault. The car switches to petrol and drives on, so the only symptom may be that it runs on petrol more than it used to — worth noticing, because the alternative-fuel system's faults do not announce themselves any louder than this.
Likely causes
Start here
- Faulty alternative fuel tank level sensor · specialist
- Restricted alternative fuel filter · moderate
Less common
- Faulty alternative fuel pressure regulator · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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- The car — make, model, year and engine. The same fault behaves differently on each.
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